The present invention relates to an arrangement for displacing a closure of an opening in a cassette accommodating photosensitive material between closed and opened positions, the arrangement being particularly suited for use in a device for exposing an image, such as an image of a data carrier, onto the photosensitive material through the opening.
Devices of the last-mentioned type are already known and usually they are equipped with a projecting arrangement which projects the image of the data carrier onto the photosensitive material, such as film, accommodated in the cassette, through the opening which is unobstructed by the closure while the projection of the image takes place, with an opening arrangement which is operative for unlatching the closure which, in order to avoid accidental displacement thereof towards its open position during the transportation or the handling of the cassette, is latched in its closed position, and for displacing the closure from its closed position into its open position and then back into its closed position after the image-projecting operation has been concluded, as well as with a control arrangement which controls the performance of the unlatching, opening, projecting and closing operations in the desired sequence. In some of the conventional constructions of the opening arrangement, the latter includes a carriage which carries an entraining member that engages the closure and/or the latching means therefor, the carriage being movable in opposite directions along the path of displacement of the closure relative to the cassette which is properly positioned in the aforementioned device so that the entraining member entrains the closure for joint travel with the same and with the carriage from its closed into its open position and then back to its closed position in which the closure light-tightly obstructs the opening of the cassette.
One opening arrangement of this type has been disclosed in the German published publication DE-AS No. 20 21 494, wherein the entraining member is arranged on a holder which is pivotally mounted on the carriage, the axis of pivoting of the holder relative to the carriage extending normal to the direction of displacement of the carriage. A helical spring applies torque to the holder. In addition thereto, the holder is equipped with a guiding roller which is lifted as it engages the cassette during the initial phase of the displacement of the carriage towards its position corresponding to the open position of the closure until the roller engages the top surface of the cassette, which results in the pivoting of the holder relative to the carriage toward and into the position in which the entraining member engages the closure of the cassette.
Such a construction is relatively complicated and, as a result of that, also prone to malfunction. The radius of pivoting of the entraining member is relatively small, so that it can easily happen that the entraining member will engage the edge of a bore which is provided in the cassette closure for accommodating the entraining member. In addition thereto, the proper functioning of the pivoting mechanism can be assured only when the cassettes have substantially the same thickness or height. In addition thereto, there exists the danger that, when the closure offers substantial resistance to movement, or when the closure becomes stuck or jammed, the entraining member is expelled from the bore in the closure against the action of the spring which biases the same into the bore. If this effect occured during the displacement of the closure towards its closed position, the entraining member would contact and scratch the photosensitive material present in the cassette and the cassette would finally be removed from the device with the closure still in its partially or fully open position. Then, in the event that the photosensitive material has already been previously exposed with an image, such as an x-ray image, the original image-forming operation would have to be repeated, which would, in the example given, expose the patient to additional amounts of radiation. Thus, it may be seen that the conventional construction of the opening arrangement leaves much to be desired.